Objective The application of air screw drilling technology in gas drainage borehole within soft coal seam presents challenges, including severe dust pollution, low drill bit lifespan, and great difficulty in borehole purification. The use of air screw foam drilling technology is an effective way to solve the problem. A foam generator with good foaming performance is one of the keys to implementing the foam drilling technology. However, most current foam generators could not meet the requirements.
Methods In response to this issue, a small-sized foam generator was designed based on the spiral foam generator, with an air kinetic energy conversion device increased. Besides, the rationality of the structural design of the air kinetic energy conversion device and the installation angle of the stirring blades in the turbine stirring section were evaluated and optimized using the numerical simulation analysis methods.
Results and Conclusions The results show that: (1) The air kinetic energy conversion device could effectively drive the main shaft of the foam generator to rotate, achieving an average rotational speed 621.61 r/min under 0.8 MPa air pressure. (2) After the kinetic energy conversion, the gas can enter the foam generator continuously and mix with the foam base liquid to achieve the design purpose. (3) By comparing and analyzing the trace distribution of the mixed phase, turbulence distribution in the fluid domain, gas phase distribution and bubble size distribution, it is found that a stirring blade with an installation angle of 30° has good stirring efficiency and gas-liquid mixing effect. The research results have established a foundation for the successful application of air screw foam drilling technology in gas drainage boreholes within soft coal seams.
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